Offset drift compensation

ABSTRACT

An offset drift compensation circuit for correcting offset drift that changes with temperature. In one example, offset drift compensation circuit includes a low temperature offset compensation circuit and a high temperature offset circuit. The low temperature offset compensation circuit is configured to compensate for drift in offset at a first rate below a selected temperature. The high temperature offset compensation circuit is configured to compensate for drift in offset at a second rate above the selected temperature. The first rate is different from the second rate.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This continuation application claims priority to U.S. patent applicationSer. No. 15/934,467, filed Mar. 23, 2018, which is incorporated hereinby reference in its entirety.

BACKGROUND

Various analog circuits, amplifiers for example, suffer from offseterror. Offset error results from mismatch of circuit components. Forexample, mismatch of differential input transistors can cause anamplifier to produce a non-zero output voltage when the amplifier inputvoltage is zero. Offset error can detrimentally affect the operation ofa circuit receiving a signal that includes an offset voltage.

Attempts are made to minimize offset error in a variety applications.However, even after compensating for offset error, the factors thatproduce the offset error can vary with temperature, causing a variationin the offset error with temperature. Such variation is referred to as“offset drift.”

SUMMARY

Offset drift compensation circuits that correct for offset that changeswith temperature are disclosed herein. In one example, an offset driftcompensation circuit includes a low temperature offset compensationcircuit and a high temperature offset compensation circuit. The lowtemperature offset compensation circuit is configured to compensate fordrift in offset at a first rate below a selected temperature. The hightemperature offset compensation circuit is configured to compensate fordrift in offset at a second rate above the selected temperature. Thefirst rate is different from the second rate.

In another example, an amplifier includes an amplification stage and anoffset drift compensation circuit. The offset drift compensation circuitis coupled to the amplification stage. The offset drift compensationcircuit is configured to provide an offset compensation current to theamplification stage. The offset compensation current cancels offsetgenerated by the amplification stage that changes with temperature. Theoffset compensation current changes at a first rate responsive totemperature above a selected temperature. The offset compensationcurrent changes at a second rate responsive to temperature below theselected temperature.

In a further example, an asymmetric offset drift compensation circuitincludes a low temperature offset compensation circuit and a hightemperature offset circuit. The low temperature offset compensationcircuit includes first bandgap voltage circuit, and a first base-emittervoltage circuit. Current flows through the first bandgap voltage circuitto the first base-emitter voltage circuit. Current flowing through thefirst bandgap voltage circuit is set to cause the low temperature offsetcompensation circuit to generate a first offset compensation rampvoltage starting at a first temperature. The high temperature offsetcompensation circuit includes a second bandgap voltage circuit, and asecond base-emitter voltage circuit. Current flows through the secondbase-emitter voltage circuit to the second bandgap voltage circuit.Current flowing through the second bandgap voltage circuit is set tocause the high temperature offset compensation circuit to generate asecond offset compensation ramp voltage starting at a secondtemperature.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various examples, reference will now bemade to the accompanying drawings in which:

FIG. 1 shows a block diagram for an example of an amplifier thatincludes offset drift compensation in accordance with the presentdisclosure;

FIG. 2 shows a block diagram for an example of a low temperature offsetdrift compensation circuit in accordance with the present disclosure;

FIG. 3 shows a schematic diagram for an example of a bandgap voltagecircuit in accordance with the present disclosure;

FIG. 4 shows a schematic diagram for an example of a base-emittervoltage circuit in accordance with the present disclosure;

FIG. 5 shows a schematic diagram for an example of a current mirrorcircuit in accordance with the present disclosure;

FIG. 6 shows an example of setting a knee point in an offset driftcompensation circuit in accordance with the present disclosure;

FIG. 7 shows examples of offset correction produced by a low temperatureoffset drift compensation circuit in accordance with the presentdisclosure;

FIG. 8 shows a block diagram for an example of a high temperature offsetdrift compensation circuit in accordance with the present disclosure;

FIG. 9 shows examples of offset correction produced by a hightemperature offset drift compensation circuit in accordance with thepresent disclosure; and

FIG. 10 shows examples of offset correction produced by a lowtemperature offset drift compensation circuit and a high temperatureoffset drift compensation circuit in accordance with the presentdisclosure.

DETAILED DESCRIPTION

Certain terms have been used throughout this description and claims torefer to particular system components. As one skilled in the art willappreciate, different parties may refer to a component by differentnames. This document does not intend to distinguish between componentsthat differ in name but not function. In this disclosure and claims, theterms “including” and “comprising” are used in an open-ended fashion,and thus should be interpreted to mean “including, but not limited to .. . .” Also, the term “couple” or “couples” is intended to mean eitheran indirect or direct wired or wireless connection. Thus, if a firstdevice couples to a second device, that connection may be through adirect connection or through an indirect connection via other devicesand connections. The recitation “based on” is intended to mean “based atleast in part on.” Therefore, if X is based on Y, X may be a function ofY and any number of other factors.

To compensate for circuit offset, the offset is measured and under knownconditions (e.g., at an optimal operating temperature), and subtractedfrom the output of the circuit during operation. Unfortunately, suchcompensation does not correct for offset drift over temperature. Tocompensate for offset drift, some circuits determine the slope of offsetover temperature and apply the slope to compensate for offset drift.Such compensation cannot correct for second order effects that arecaused by mechanical stress related to temperature or other temperaturerelated effects. Other circuits apply digital correction that selects atrim value based on measured temperature. Such correction can produceundesirable discontinuities in an analog signal.

The present disclosure includes offset drift correction circuitry thatindependently trims offset drift at high temperatures and lowtemperatures without discontinuities and without affecting the offset atroom temperature. Implementations of the circuits disclosed hereinprovide offset drift correction for analog circuitry that is affected bypackage stress or in which offset changes with bias conditions leadingto different offset drift at high temperatures relative to lowtemperatures.

FIG. 1 shows a block diagram for an example of an amplifier 100 thatincludes offset drift compensation in accordance with the presentdisclosure. The amplifier 100 includes an amplification stage 102, a lowtemperature offset compensation circuit 104, a high temperature offsetcompensation circuit 106, and a resistor 108. While a singleamplification stage 102 is illustrated in FIG. 1, some implementationsof the amplifier 100 include multiple amplification stages. Theamplification stage 102 receives as input a differential signal IN+/IN−,and applies a gain to the received signal to produce an output signal110. The output signal 110 is a current that produces an output voltageof the amplification stage 102 across the resistor 108. Theamplification stage 102 (via the output signal 110) also generates anoffset voltage across the resistor 108. The offset voltage varies withthe temperature of the amplifier 100.

To compensate for the temperature variable offset produced by theamplification stage 102, the amplifier 100 includes the low temperatureoffset compensation circuit 104 and the high temperature offsetcompensation circuit 106. The low temperature offset compensationcircuit 104 and the high temperature offset compensation circuit 106form an asymmetric offset drift compensation circuit 116 that is coupledto the amplification stage 102. The low temperature offset compensationcircuit 104 and the high temperature offset compensation circuit 106 arecoupled to the resistor 108, and produce a voltage drop across theresistor 108 that compensates for the offset generated by theamplification stage 102. Below a selected temperature the lowtemperature offset compensation circuit 104 generates a cold trimcurrent 112 that produces an offset compensation voltage across theresistor 108, and above the selected voltage, the high temperatureoffset compensation circuit 106 generates a current that produces anoffset compensation voltage across the resistor 108. Above the selectedvoltage, the low temperature offset compensation circuit 104 does notgenerate a cold trim current 112 that produces an offset compensationvoltage across the resistor 108, and below the selected voltage, thehigh temperature offset compensation circuit 106 does not generate a hottrim current 114 that produces an offset compensation voltage across theresistor 108.

In some implementations, the rate of change of the offset compensationproduced by the low temperature offset compensation circuit 104 isdifferent from the rate of change of the offset compensation produced bythe high temperature offset compensation circuit 106 to compensate forvarying rates of change in the offset produced by the amplificationstage 102 over temperature. While the amplifier 100 is illustrated inFIG. 1 as included one low temperature offset compensation circuit 104and one high temperature offset compensation circuit 106, someimplementations of the amplifier 100 include more than one lowtemperature offset compensation circuit 104 and/or more than one hightemperature offset compensation circuit 106, where each low temperatureoffset compensation circuit 104 and high temperature offset compensationcircuit 106 compensates for a different rate of change in the offsetproduced by the amplification stage 102 over temperature.

While FIG. 1 illustrates use of the low temperature offset compensationcircuit 104 and the high temperature offset compensation circuit 106 toprovide offset drift compensation to an amplification stage 102,implementations of the low temperature offset compensation circuit 104and the high temperature offset compensation circuit 106 are applicableto various electronic circuits that are subject to offset drift. Forexample, the low temperature offset compensation circuit 104 and hightemperature offset compensation circuit 106 are applicable to compensatefor offset drift in a comparator circuit.

FIG. 2 shows a block diagram for an example of the low temperatureoffset compensation circuit 104 in accordance with the presentdisclosure. The low temperature offset compensation circuit 104 includesa band-gap voltage circuit 202, a base-emitter voltage circuit 204, anda current mirror 206. The current mirror 206 includes a current outputdigital-to-analog converter 208. The band-gap voltage circuit 202 iscoupled to a power supply. The base-emitter voltage circuit 204 iscoupled to a current output of the band-gap voltage circuit 202. Theband-gap voltage circuit 202 includes transistors and other electroniccomponents, and generates a current output that is generally constantwith respect to temperature. For example, the band-gap voltage circuit202 generates a current as a function of bandgap voltage (V_(bg)), whichis generally constant with respect to temperature.

FIG. 3 show a schematic for an example of the band-gap voltage circuit202. The illustrated example of the 202 includes bipolar transistors 302and 304, amplifier 306 and resistors 308, 310, 312, and 314 arranged togenerate V_(bg) and amplifier 316, transistor 318, and resistor 320 togenerate a current proportional to V_(bg). The transistor 302 may be anN-emitter version of the transistor 304. The collectors of thetransistors 302 and 304 are coupled to a voltage source via theresistors 308 and 310 respectively. The amplifier 306 drives the basesof the transistors 302 and 304 to equalize the collector currents of thetransistors 302 and 304. The voltages across resistors 312 and 314 areproportional to absolute temperature (PTAT), and the base-emittervoltage of transistor 304 is complementary to absolute temperature(CTAT). The PTAT voltage across resistor 314 is scaled to becomplementary to the CTAT voltage (V_(be) of transistor 304). Thevoltage output of the amplifier 306 is a sum of the CTAT voltage andscaled PTAT voltage, and is constant with temperature. The amplifier316, the transistor 318, and the resistor 320 are coupled to convertV_(bg) output by the amplifier 306 to a current V_(bg)/R.

The base-emitter voltage circuit 204 includes transistors and otherelectronic components, and generates a base-emitter voltage (V_(be)) anda corresponding current that varies approximately linearly as a functionof temperature. The signal 210 is the difference of the bandgap voltagegenerated by the band-gap voltage circuit 202 and the base-emittervoltage generated by the base-emitter voltage circuit 204 (e.g., thesignal 210 is V_(bg)−V_(be)).

FIG. 4 shows a schematic diagram for an example of the base-emittervoltage circuit 204. The illustrated example of the base-emitter voltagecircuit 204 includes a current source 402, a transistor 404 to generatethe base-emitter voltage V_(be), and an amplifier 406, a transistor 408,and a resistor 410 to convert V_(be) to a proportional current. Thetransistor 404 is connected as a diode with the emitter connected toground. The voltage at the base of the transistor 404 varies as afunction of temperature. The amplifier 406, the transistor 408, and theresistor 410 are coupled to convert V_(be) generated by the transistor404 to a current V_(be)/R.

The signal 210 drives the current mirror 206. The output of the currentmirror 206 is the cold trim current 112 that compensates for offsetdrift when converted to a voltage across the resistor 108. The currentmirror 206 includes the current output digital-to-analog converter 208to set the slope (i.e., the rate of change) of an offset compensationramp current of the cold trim current 112. For example, animplementation of the current output digital-to-analog converter 208includes a plurality of transistors that are switchable to providecurrent through the current mirror 206 to the cold trim current 112. Thegreater the number of transistors, or the larger the transistors,selected the greater the current flowing into the current mirror 206 andthe greater the slope of the cold trim current 112 generated based onthe signal 210.

FIG. 5 shows an example of the current mirror 206. The current mirror206 includes transistor 502, 504, 506, 508, 510, 512, and the currentoutput digital-to-analog converter 208, which includes a number oftransistors 516 and switches 514. Current flowing in the transistors 502and 504 is a function of the currents generated by the bandgap voltagecircuit 202 and the base-emitter voltage circuit 204, and is reflectedin the current flowing in the transistors 506 and 508. In the currentoutput digital-to-analog converter 208, the switches 516 are selectablyopened or closed (e.g., during manufacturing trim of the amplifier 100)to set the current flowing into the transistor 510 and set the slope ofthe cold trim current 112. The transistors 510 and 512 are coupled as acurrent mirror, wherein the current flowing in the transistor 510 isreflected in the transistor 512.

In manufacture, the circuitry of the low temperature offset compensationcircuit 104 is adjusted (trimmed) to control the offset driftcompensation provided at low temperatures. For example, animplementation of the band-gap voltage circuit 202 includes adigital-to-analog converter that adjusts the output of the band-gapvoltage circuit 202 to set the voltage at which the base-emitter voltagecircuit 204 output exceeds the band-gap voltage circuit 202 output. Thevoltage at which the base-emitter voltage circuit 204 output exceeds theband-gap voltage circuit 202 output corresponds to a selectedtemperature value because the base-emitter voltage circuit 204 outputvaries with temperature. Such adjustment may be referred to as setting a“knee point” in the cold trim current 112 because at temperatures abovethe knee point the low temperature offset compensation circuit 104 hasno effect on offset drift, and at temperatures below the knee point thelow temperature offset compensation circuit 104 compensates for offsetdrift as a function of temperature. FIG. 6 shows an example of settingthe knee point in the low temperature offset compensation circuit 104 inaccordance with the present disclosure. In FIG. 6, V_(bg) 610 isconstant across temperature, and is adjustable in a range 604. V_(be)402 varies with temperature. The temperature at which V_(be) 602intersects V_(bg) 610 is the knee point temperature. Accordingly, byadjusting V_(bg) 610 over the range 604, the knee point temperature isadjustable over the range 608. The cold trim current 112 is representedby the signal 606, which shows that at temperatures below the knee pointtemperature the cold trim current 112 compensates for offset drift as afunction of the V_(be) 602, and at temperatures above the knee pointtemperature, the cold trim current 112 does not compensate for offsetdrift. Accordingly, room temperature offset compensation applies attemperatures above the knee point, and the knee point is set provideoffset drift compensation at temperatures below those at which the roomtemperature offset compensation is effective.

In addition to the temperate at which offset drift compensation isapplied (i.e., the knee point temperature), the low temperature offsetcompensation circuit 104 is trimmed to set the slope of the offset driftcompensation. Referring again to FIG. 4, the slope of the signal 606 isa function of the slope of the signal V_(be) 602. To compensate for therate of change of the offset drift of the amplification stage 102, thecurrent output digital-to-analog converter 208 is used to vary the slopeof the cold trim current 112 generated by the current mirror 206 as afunction of the signal 210. In manufacture, the rate of change of theoffset drift of the amplification stage 102 is measured with decreasingtemperature and the current output digital-to-analog converter 208 isset to generate a current in the current mirror 206 that produces a coldtrim current 112 that best cancels the offset drift with decreasingtemperature. FIG. 7 shows examples of offset correction produced by thelow temperature offset compensation circuit 104. At temperature 718 (theknee point) and below, the low temperature offset compensation circuit104 begins to compensate for offset drift. Using the current outputdigital-to-analog converter 208, any one of a variety of compensationslopes is selectable to best compensate for the offset drift produced bythe amplification stage 102. In FIG. 7, the current outputdigital-to-analog converter 208 selectably provides eight compensationslopes 702, 704, 706, 708, 710, 712, 714, and 716 in addition to thezero slope 700. Implementations of the current mirror 206 applyinversion to produce slopes 720 based on the slopes 702, 704, 706, 708,710, 712, 714, and 716. Some implementations of the current mirror 206include a current output digital-to-analog converter 208 that produces adifferent number of compensation slopes.

FIG. 8 shows a block diagram for an example of a high temperature offsetcompensation circuit 106 in accordance with the present disclosure. Thehigh temperature offset compensation circuit 106 includes a band-gapvoltage circuit 802, a base-emitter voltage circuit 804, and a currentmirror 806. In some implementations of the 104, the band-gap voltagecircuit 802 is similar to the band-gap voltage circuit 202, the baseemitter voltage circuit 304 is similar to the base emitter voltagecircuit 204, and the current mirror 806 is similar to the current mirror206. The current mirror 806 includes a current output digital-to-analogconverter 808. The base-emitter voltage circuit 804 is coupled to apower supply. The band-gap voltage circuit 802 is coupled to a currentoutput of the base-emitter voltage circuit 804. The band-gap voltagecircuit 802 includes transistors and other electronic components, andgenerates a current output that is generally constant with respect totemperature. For example, the band-gap voltage circuit 802 generates acurrent as a function of bandgap voltage (V_(bg)), which is generallyconstant with respect to temperature.

The base-emitter voltage circuit 804 includes transistors and otherelectronic components, and generates a base-emitter voltage (V_(be)) anda corresponding current that varies approximately linearly as a functionof temperature. The signal 810 is the difference of the bandgap voltagegenerated by the band-gap voltage circuit 802 the base-emitter voltagegenerated by the base-emitter voltage circuit 804 (e.g., the signal 810is V_(be)−V_(bg)).

The signal 810 drives the current mirror 806. The output of the currentmirror 806 is the hot trim current 114 that compensates for offset driftwhen converted to a voltage across the resistor 108. The current mirror806 includes the current output digital-to-analog converter 808 to setthe slope (i.e., the rate of change) of an offset compensation rampcurrent of the hot trim current 114. For example, implementations of thecurrent output digital-to-analog converter 808 include a plurality oftransistors that are switchable to provide current through the currentmirror 806 to the hot trim current 114. The greater the number oftransistors, or the larger the transistors, selected the greater thecurrent flowing into the current mirror 806 and the greater the slope ofthe hot trim current 114 generated based on the signal 810.

In manufacture, the circuitry of the high temperature offsetcompensation circuit 106 is adjusted (trimmed) to control the offsetdrift compensation provided at high temperatures. For example,implementations of the band-gap voltage circuit 802 include adigital-to-analog converter that adjusts the output of the band-gapvoltage circuit 802 to set the voltage at which the base-emitter voltagecircuit 804 output exceeds the band-gap voltage circuit 802 output. Thevoltage at which the base-emitter voltage circuit 804 output exceeds theband-gap voltage circuit 802 output corresponds to a selectedtemperature value because the base-emitter voltage circuit 804 outputvaries with temperature. Such adjustment may be referred to as setting a“knee point” in the hot trim current 114 because at temperatures belowthe knee point the high temperature offset compensation circuit 106 hasno effect on offset drift, and at temperatures above the knee point thehigh temperature offset compensation circuit 106 compensates for offsetdrift as a function of temperature. Setting of the knee pointtemperature in the high temperature offset compensation circuit 106 isperformed as described with respect to the low temperature offsetcompensation circuit 104. The output of the band-gap voltage circuit 802is adjusted to set the temperature at which V_(be) intersects V_(bg). Attemperatures below the knee point temperature the hot trim current 114compensates for offset drift as a function of V_(be), and attemperatures above the knee point temperature, the hot trim current 114does not compensate for offset drift. Accordingly, room temperatureoffset compensation applies at temperatures below the knee point, andthe knee point is set provide offset drift compensation at temperaturesabove those at which the room temperature offset compensation iseffective. In some implementations, the knee point temperature selectedfor the high temperature offset compensation circuit 106 is differentthan the knee point temperature selected for the low temperature offsetcompensation circuit 104. For example, the knee point temperatureselected for the high temperature offset compensation circuit 106 may beany number of degrees higher than the knee point temperature selectedfor the low temperature offset compensation circuit 104, with roomtemperature offset compensation applied in the range between the kneepoint temperature selected for the high temperature offset compensationcircuit 106 and the knee point temperature selected for the lowtemperature offset compensation circuit 104

In addition to the temperate at which offset drift compensation isapplied, the high temperature offset compensation circuit 106 is trimmedto set the slope of the offset drift compensation. To compensate for therate of change of the offset drift of the amplification stage 102, thecurrent output digital-to-analog converter 808 is used to vary the slopeof the hot trim current 114 generated by the current mirror 806 as afunction of the signal 810. In manufacture, the rate of change of theoffset drift of the amplification stage 102 is measured with increasingtemperature and the current output digital-to-analog converter 808 isset to generate a current in the current mirror 806 that produces a hottrim current 114 that best cancels the offset drift with increasingtemperature. FIG. 9 shows examples of offset correction produced by thelow temperature offset compensation circuit 104. At temperature 918 (theknee point) and above, low temperature offset compensation circuit 104begins to compensate for offset drift. Any one of a variety ofcompensation slopes is selectable to best compensate for the offsetdrift produced by the amplification stage 102. In FIG. 9, the currentoutput digital-to-analog converter 808 selectably provides eightcompensation slopes 902, 904, 906, 908, 910, 912, 914, and 916 inaddition to the zero slope 900. Some implementations of the currentmirror 806 apply inversion to produce slopes 920 based on the slopes902, 904, 906, 908, 910, 912, 914, and 916. Some implementations of thecurrent mirror 806 include a current output digital-to-analog converter808 that produces a different number of compensation slopes.

FIG. 10 shows examples of offset drift correction produced by the lowtemperature offset compensation circuit 104 and the high temperatureoffset compensation circuit 106 in accordance with the presentdisclosure. In FIG. 10, a temperature corresponding to the knee point1002 is selected for the low temperature offset compensation circuit104, and a temperature corresponding to knee point 1004 is selected forthe high temperature offset compensation circuit 106. At temperaturesbetween the knee point 1002 and the knee point 1004 (e.g., at roomtemperature 1010), the low temperature offset compensation circuit 104and the high temperature offset compensation circuit 106 provide nooffset drift compensation and a room temperature offset compensation isapplied. At temperatures below the knee point 1002, the low temperatureoffset compensation circuit 104 generates the cold trim current 112,which includes one of the offset drift compensation ramp voltages 1006selected to best correct low temperature offset drift generated by theamplification stage 102. At temperatures above the knee point 1004, thehigh temperature offset compensation circuit 106 generates the hot trimcurrent 114, which corresponds to one of the offset drift compensationramp voltages 1008 selected to best correct high temperature offsetdrift generated by the amplification stage 102.

The above discussion is meant to be illustrative of the principles andvarious implementations of the present invention. Numerous variationsand modifications will become apparent to those skilled in the art oncethe above disclosure is fully appreciated. It is intended that thefollowing claims be interpreted to embrace all such variations andmodifications.

What is claimed is:
 1. An offset drift compensation circuit, comprising:a low temperature offset compensation circuit configured to compensatefor drift in offset at a first rate below a selected temperature; and ahigh temperature offset compensation circuit configured to compensatefor drift in offset at a second rate above the selected temperature;wherein the first rate is different from the second rate.
 2. The offsetdrift compensation circuit of claim 1, wherein the low temperatureoffset compensation circuit is configured to: generate an offsetcompensation ramp voltage starting at a first temperature that is lessthan or equal to the selected temperature; and generate a fixed offsetcompensation voltage responsive to temperature above the firsttemperature.
 3. The offset drift compensation circuit of claim 2,wherein the low temperature offset compensation circuit comprises abandgap voltage circuit and a base-emitter voltage circuit, wherein:current flows through the bandgap voltage circuit to the base-emittervoltage circuit; and current flowing through the bandgap voltage circuitis set to determine the first temperature.
 4. The offset driftcompensation circuit of claim 1, wherein the high temperature offsetcompensation circuit is configured to: generate an offset compensationramp voltage starting at a second temperature that is higher than orequal to the selected temperature; and generate a fixed offsetcompensation voltage responsive to temperature below the secondtemperature.
 5. The offset drift compensation circuit of claim 4,wherein the high temperature offset compensation circuit comprises abandgap voltage circuit and a base-emitter voltage circuit, wherein:current flows through the base-emitter voltage circuit to the bandgapvoltage circuit; and current flowing through the bandgap voltage circuitis set to determine the second temperature.
 6. The offset driftcompensation circuit of claim 4, wherein the second temperature ishigher than the first temperature.
 7. The offset drift compensationcircuit of claim 4, further comprising: a first current digital toanalog converter configured to set a rate of change of the offsetcompensation ramp voltage starting at the first temperature; and asecond current digital to analog converter configured to set a rate ofchange of the offset compensation ramp voltage starting at the secondtemperature.
 8. The offset drift compensation circuit of claim 1,further comprising a current mirror circuit coupled to the lowtemperature offset compensation circuit and the high temperature offsetcircuit.